Would rhodos or hydrangeas survive in containers (like large barrels), or do they have to be planted in the ground to survive? If so, how large of a container would be needed? And are there different kinds of these plants that would be better suited to growing in a container? Even though I live in the suburbs of Vancouver, we still get more snow than the rest of the Lower Mainland in the winter -- would this pose more of a hazard to the plants if they are in containers? Thanks.
All hardy cultivars should be suitable. Choose ones with compact growth habits and hardiness ratings indicating tolerance of temperatures lower than usual for your area, to compensate for them being in containers.
I have, in zone 5b, notice that hydrangeas do very well in pots, if you follow the general drainage/moisture control/fertilizing concepts for the plant. You should be able to find, in a decent book, lists of problems for families or specific plants if any special occur for containers. Always remember to use a clean pot - light soap and a couple of rinses. If you suspect mould, take care of it and don't use it that season. If the pot is large enough, I have kept hardies outside longer with an 'expansion' idea. I use 16 oz to 2 Lieter botles in the bottom of pots to help reduce weight, and I colapse one or two of the bottles before sealing it. As the weather warms, and the pot does, the bottles expand, and collapsing a few allow them to flex more with this. As the weather cools, the reduce in size, allowing for contraction with cooler air - this is the important part. As the soil cools, if a large part has soil in contact with the ground, small ice crystals will form, harming roots and pot. This collaps helps give space for thos crystals and an insulated space. Finally, watch with care in cooler weather with Terra Cotta, and warmer weather with concrete. Allow for slight changes in watering for these changes to avoid cracks or too much drying respectively
Actually the problem with overwintering plants in containers is that part of the soil mass has air outside the pot walls instead of all the roots being in the soil. Pots sitting on the ground are better than those up on a deck because these at least get the warmth from the soil where the bottom of the pot touches it. I would definitely not put anything in the pot to interfere with it being warmed by sitting on the ground. Freezing of the soil inside the pot is dealt with by insulating the walls of the pot during cold weather. Freezing and cracking of pot walls is prevented by drying them out thoroughly and then coating them with a waterproofing material.
Thanks!- that was an accident from last year (I got lazy about a 30" terra cotta container) that almost worked, and was running an actual experiment this year. I had the pots on concrete near a light wall, west sun. I had thought about sealing, but my only experience is with wood, and I worried about biologically safe coatings. I will just bring the pots in near a heat source, and follow your suggestions for next season!
